Variable yield, or dial-a-yield, is an option available on most modern nuclear weapons.
For example, the Mod-10 B61 bomb had selectable explosive yields of 0.3, 5, 10 or 80 kilotons, depending on how the ground crew set a dial inside the casing when it was loaded onto an aircraft.
Examples of variable yield weapons include the B61 nuclear bomb family, B83, B43, W80, W85, and WE177A warheads.
Most modern nuclear weapons are Teller–Ulam design type thermonuclear weapons, with a fission primary stage and a fusion secondary stage that is collapsed by the energy from the primary.
[2] A dial-a-yield device is featured in the plot of the thriller novel Diablo Mesa.